Not the person you responded to, but I can try to offer some suggestions. At a glance I take it the community you're talking about is Invincible, but I don't see any posts where you've tried to direct people to the community.

I'd recommend posting to !newcommunities@lemmy.world, despite it not being new anymore, and !communitypromo@lemmy.ca. So far as I can tell, these seem to be two of the larger and relatively more active communities for this.

I'd also suggest subscribing to !asklemmy@lemmy.world and !asklemmy@lemmy.ml to keep an eye out for if/when people ask about shows people are enjoying or even just outright for communities for [insert show]. For the latter especially I'd also suggest subscribing to !lemmy411@lemmy.ca, which while not as active is where occasionally you'll see people explicitly looking for communities, giving you a great opportunity to point them to your community if it's relevant.

Beyond this, maybe cross-post some of the threads to relevant and/or broader communities, so say cross-post some of your Invincible threads (after a bit of time, so as to not seem spammy, some people browsing can be really picky about this) to other communities. For instance you might cross-post some of these to !casualconversation@lemmy.world or !general@lemmy.world or other instances' general discussion/chat communities if they don't have a tv/show community to cross-post to, supposing that it's okay by their rules.

I'd recommend adjusting them a little to better fit the vibes of the relevant communities you're cross-posting to for better reception btw, so it doesn't feel like you're just tossing stuff at'em. Altogether it's admittedly a lot, but I don't think anyone's ever said community building is a little. Best of luck!